1. Field of the Invention
This invention relates to sorption containers, and more particularly to a sorption container and method for regenerative heat exchange between at least two sorption containers.
2. Description of the Prior Art
Typically, in devices and methods providing regenerative heat exchange, a light volatile operating agent is absorbed by a heavier volatile sorption agent as a result of a release of heat energy. The light volatile operating agent can then be subsequently desorbed or separated from the heavier volatile sorption agent as a result of heat adsorption by the sorption agent. The sorption agent may be in liquid as well as in solid form. When using a liquid sorption agent that has become enriched with operating agent, the sorption agent can be pumped between the sorption container which functions as an adsorber and the sorption container which functions as a desorber. During thermal cycling, both the light volatile operating agent and the heavier volatile sorption agent remain in the same container depending on the temperature level which is maintained by the adsorber container and the desorber container. In order for the operating agent to be expelled from the sorption agent, the adsorber container along with the sorption agent and heat exchangers must be heated from a relatively low adsorption temperature to a relatively high desorption temperature and subsequently cooled.
While a heat exchange between solutions that are poor and rich with liquid sorption agents is possible in a relatively simple manner using separate heat exchangers, this can usually only be achieved under very special conditions when solid sorption substances are utilized.
Suggestions to overcome this limitation are found in German Patent No. DE-OS 3207656.8. In this reference, a portion of the sorption agent heat and container heat is transmitted between the two sorption agent containers by means of a heat carrier medium and a relatively expensive apparatus that couples the two sorption medium containers. As a result, it is possible to partially transfer the heat of operation in order to heat the sorption agent and expel the operating medium while forcing it into a second sorption container during its cooling process. As a result, less operating heat has to be generated in order to heat the second sorption medium container. Therefore, the system is able to exchange as much heat as desirable between the two sorption medium containers. In devices such as the one described above, the relationship between the cold that is generated with respect to the heat that is generated can be greatly improved.
An alternative device for exchanging heat between two sorption medium containers is described in "Zeolites: Facts, Figures, Future"; by P.A. Jacobs and R.A. Van Santen on page 519, published in 1989 by Elsevier Science Publishers, B.V. Amsterdam. In this reference, two sorption medium containers are heated by oil. During a first phase, the oil coming from the first sorption medium container is heated in a heater, and flows into the second sorption medium container. The oil is cooled in the second sorption medium container due to the fact that the sorption medium therein absorbs the heat energy. This causes the sorption medium in the second sorption medium container to desorb the operating medium. The oil is subsequently cooled a second time by an oil/air heat exchanger and then provided to the first sorption container by a circulation pump. The oil which is now located in the first sorption container absorbs the heat from the first container thereby cooling the sorption medium contained therein. During the next phase of operation, the oil flow direction is reversed so that unheated oil is provided by the circulation pump to the second sorption medium container wherein the oil is heated while the sorption medium in the second container is cooled. The oil is then sent from the second sorption medium container to the heater where the oil is heated and then pumped into the first sorption medium container. Therein, the heat of the oil is absorbed by the sorption medium of the first container which will cool the oil. Hence, by utilizing this oil cycle, a sorption medium container is cooled and another is heated while the heat losses are only equalized by the heater. This can only be achieved when the sorption medium container heat exchangers are designed so that the heat emitted by the oil is consistently provided to the lowest temperature portions of the sorption medium. This requires maintaining a slowly progressing and severely limited temperature variation along the heat exchanger surface.
The above requirements result in a heat exchanger design wherein only a relatively small area of the face of the heat exchanger transfers heat between the oil and the sorption medium. As a result, the remaining portion of the heat exchanger face is ineffective during the individual partial operating phases. In practical applications, extremely large heat exchanger faces are required which can correspondingly cost a significant amount.
Installations of this type have additional disadvantages. First, only the sorption medium filling that is in close proximity to the hot oil inlet within a sorption medium container is heated. The boundary of the resulting desorption front within the sorption medium will subsequently traverse through all of the sorption medium filling if enough heat is provided. During the heating of the sorption medium, the operating medium is normally desorbed. However, since some areas of the sorption medium may not be heated to the critical desorption temperature level, any desorbed operating medium will not be expelled and liquified into an operating medium steam trough as desired. Instead, the unheated portions of the sorption medium will readsorb the operating medium that is expelled by the heated sorption medium areas. This causes the first operating medium steam that is liquified to be provided to the operating medium steam trough only after heating the sorption medium for a relatively long time after the individual partial operating phase has begun.
Tests have shown that this relatively long heating time may be up to 50% of the total cycle time. Due to the readsorption of the operating medium, the areas of the sorption medium which have not yet been heated by the oil are later heated. The oil is undesirably heated by these heated sorption areas before leaving the sorption medium container. The required severe and limited temperature gradient during the oil cycle is therefore significantly effected. The same negative effect correspondingly occurs in the adsorption phase.
A further disadvantage consists in that due to the relatively slow flow of oil and the long flow path in the heat exchanger, a relatively large volume of oil must be cycled in order to obtain desired results. Therefore, the system becomes so slow that approximately 30 minutes are needed before the first cold production is realized after the initial system startup. As a result, this device is not suitable for relatively short operating times or a cyclical on/off operation.
The final disadvantage is that oil is flammable. Therefore, the use of oil requires various safety measures against overflow and combustion, as well as high drive energies for the circulation pump and expensive heat exchangers for heating or cooling of the oil.